Furnace



w. s. BLAUVELT ETAL 2,345,231

FURNACE I March 28, 1944.

5 Sheets-Sheet 1 Filed Jan. 31, 1941 ATTORNEY March 28, 1944.

w. s. BLAUVELT E AL FURNACE Filed Jan. 31, 1941 3 Sheets-Sheet 2 47'TOR/V5 Y March 28, 1944. w. s. BLAUVELT ETAL 2,345,231

' FURNACE v Filed Jan. 31, 1941 5 Sheets-Sheet 3 l "J A if m I 9/ 9x .24W9; I 95 93/ ,4 7- TOR/V5 Y Patented Mar. 28, 1944 FURNACE Warren S.Blauvelt, Ann Arbor, Mich, and Nolan A. Curry, Troy, N. Y., asslgnors toBlauvelt Associates, Inc., Troy, N. Y., a corporation of New YorkApplication January 31, 1941, Serial No. 376,828 (01. 237-8) 13 Claims.

Broadly speaking, our invention particularly relates to a furnace,primarily designed for solid fuel-burning purposes, which includes aheattransfer device; and to control means for said furnace adaptedautomatically to pass the gases of combustion of the fuel in saidfurnace to the heat-transfer device when the temperature of the mediumheated thereby indicates a demand for heat and substantially to preventa flow of said gases to the heat-transfer device when the heat demandhas been satisfied. I

It is a first object of our invention to provide a furnace having aplurality of passages communicating with the combustion chamber thereof,one of said plurality of passages including a heat-transfer device and asecond of said passages constituting a by-pass, and means forcontrolling the flow of the products of combustion through saidplurality of passages.

1 Another object of our invention resides in providing a furnacecomprising a plurality of passages communicating with the combustionchamber thereof and with a stack or exhaust passage, one of saidpassages including a heat-transfer device for heating one medium and asecond of said passages including a heat-transfer device for heating asecond medium, and means responsive to the temperatures of said mediumsfor controlling the flow of the products of combustion to the respectiveheat-transfer devices.

Another object resides in providing a furnace of the character abovepointed out in which one of the plurality of passages constitutes aby-pass and in which the control means therefor is so constructed andarranged that when the temperature of one medium to be heated indicatesa demand for heat, said control means will oper-' ate to permit the gaseof combustion to flow to the heat-transfer device wherein heat isobtained for raising the temperature of said medium and forsubstantially preventing the flow of said gases through said by-pass,and, when the heat demand of the medium is satisfied, will operatesubstantially to prevent the flow of said gases to said heat-transferdevice and to permit the gases to flow through said by-pass.

Another object of our invention resides in providing a furnace andcontrols therefor of the foregoing character in which an electricallyoperated draft-producing means is employed which, when the controls sopermit, will produce a forced flow of gases of combustion througheitherthe by-pass passage or the passages including the heat-transferdevices; and in which the control means includes a stack switch orsimilar device which controls the draft producing means, irrespective ofthe other control means, to produce a draft through the by-pass and fuelbed to maintain the fuel bed temperature sufliciently high to sustaincontinued combustion of the fuel under idling conditions.

More specifically, it is an object of our invention to provide a furnaceand controls therefor of the foregoing character in which valves areemployed for controlling the flow of gases of combustion through therespective passages, the valves and the operating means therefor beingso correlated that flow of the gases through the by-pass issubstantially prevented when one of the valves opens to permit the gasesto flow through one of the heat-transfer devices, the valve for theby-pass passage being held in open position when the gases are notpermitted to flow to any of the heat-transfer devices.

With these and other objects in view, our invention includes the novelelements and the combinations and arrangements thereof described belowand illustrated in the accompanying drawings, in which preferredembodiments of our invention are shown, and in which- Fig. l is asectional, elevation view of a furnace embodying one form of ourinvention and illustrating somewhat diagrammatically the controlstherefor;

Fig. 2 is a fragmentary, sectional elevation View of the furnace of Fig.1, showing the controls actuated to provide a flow of gases ofcombustion through one of the heat-transfer devices;

Fig. 3 is a view similar to Fig. 2 but showing the controls actuated toprovide a flow of gases through a second of the heat-transfer devices;

Fig. 4 is a fragmentary, sectional elevation view showing a modifiedform of furnace and controls;

Fig. 5 is a wiring diagram of our control system illustrating somewhatschematically some of the control elements in perspective;

Fig. 6 is a wiring diagram similar to Fig. 5 but showing various of theelements in different positions; and

Y Fig. 7 is a fragmentary, sectional elevation View of our furnaceshowing a preferred location of one of the controls.

Referring to the drawings and first to Fig. 1, l indicates generally afurnace comprising a combustion chamber 2 within which fuel may burnupon a grate 3. The surface of the bed of fuel is indicated in dot-dashlines at 4. Fuel may be delivered to the fuel bed through a supplypassage or magazine 5 and air for combustion purposes is admittedthrough an opening 6 in the The passage I2 includes a heat-transferdevice,

indicated generally at I3, comprising a plurality of tubes through whichthe ases of combustion may flow and spaces about saidtubeswhich areadapted to receive air or water, for example, for house heatingpurposes. The upper end of the heat-transfer device I3 communicatesthrough an orifice I4 with a breeching or exhaust passage I 5 from whichthe gases may pass to atmosphere.

In orifice I4 is formed a seat for a valve element I6 which, ashereinafter explained, serves to control the flow of the gases throughthe passage I2 and heat-transfer device l3.

Passage I I also includes a heat-transfer device indicated generally atI! through which the gases of combustion may pass and which is adaptedto transfer heat from said gases to water, for example, for domestic hotwater purposes. The upper end of the device I! also communicates withthe breeching I5 through an orifice l8 in which is formed a seat for avalve element l9. Valve I9 serves to control the flow of gases throughpassage II and heat-transfer device II.

It will be understood that we have more or less diagrammaticallyillustrated the heat-transfor devices I3 and I! mainly for purposes ofillustration and that any type or form of heat-transfer device may beemployed.

The passage I9, in accordance with our invention, communicates withpassage 9 and with the breeching I5 and preferably does not include aheat-transfer device. The upper end of passage Ifl communicates withbreeching l5 through an orifice 26 in which is formed a seat for a valve2| which serves to control the flow of gases through passage ID.

The furnace, about the combustion chamber, passages therein andheat-transfer devices and between said devices, is preferably insulatedas illustrated and the passage I9 may be formed in the insulation.

In a furnace embodying the referred construction and relativearrangement of the passages I0, II and !2, the passage II) willcommunicate with passage 9 in a zone nearer the combustion chamher thanthose zones in which the passages l I and I2 communicate with passage 9.By relatively arranging the passages in this manner, the gases ofcombustion will flow directly to andthrough the passage I a when thevalve elements I6, I9 and 2| occupy the positions shown in Fig. 1 andthere will be no tendency of these hot gases to flow to either of thepassages I I and I2.

A fan 22, driven by motor 23, is arranged in thebreeching i5 andfunctions to provide a forced draft or fiow of gases of combustion fromthe combustion chamber and through the passages communicating therewithand with the breeching 55 when the valves so permit. The manner in whichmotor 29 and also solenoid 8 are connected in thecontrol circuit of ourfurnace will be hereinafter pointed out.

For the sake of clearness in illustration, we have shown the cables,hereinafter described, which are connected with the valves I6, I9 andIii) 2|, respectively, as passing through the upper side of thebreeching I5. It will be understood, however, that in practice, weprefer to pass the cables downwardly on the exterior of the duct and toconnect them to lever arms mounted on rods which pass through bearingsin the side of the stack, and to connect lever arms which are alsomounted on said shafts, but disposed within the breeching, with a cablewhich in turn is fastened to said valves.

As will be hereinafter more particularly pointed out, a thermostat whichis mounted in heat responsive relation to the medium such as water orair which derives its heat from the heat-transfer device I3, controls anelectrical circuit to a control motor 24 which, through the medium of aspeed-reducing mechanism 25 (see Fig. 5), drives a cam shaft 26 on whichis mounted a lever arm 21. Referring back to Fig. l, crank arm 21 isconnected through an adjustable connector 28 to a cable 29 which passesover pulleys 30 and 3| and thence downwardly and is connected to thevalve It. When the thermostat does not call for heat, arm 21 occupiesthe raised position and the valve I6 closes the orifice I4 therebypreventing the how of gases of combustion through the heat-transferdevice I3. However, when the thermostat indicates a demand for heat,motor 24 will operate to move the arm 21 through substantially 180thereby elevating the valve I6 and permitting gases to flow through thepassage I2 and heat-transfer device I3.

In accordance with our invention, the valve I6, and valve I9, ashereinafter described, are so correlated with valve 2| that when eithervalve I6 or I9 is elevated, valve 2| will be positioned to effect aclosure of the orifice 20 of passage IO, and when both valves I6 and I9are in closed position, valve 2| will lie in open position. In theembodiment illustrated, we accomplish this correlated operation of valveelements by connecting valve 2| through a cable 32 which is connected toone end of a lever arm 33, pivoted intermediate the ends at 34. To theother end of lever 33 is connected a weight 35 and a cable 36 whichpasses upwardly and over pulleys 31 and 39 and thence downwardly and isconnected to one end of a lever arm 39. Lever 39 is pivoted at a pointintermediate the ends thereof and the other end thereof is connected asindicated at 40 to the cable 29 between valve I6 and pulley 3|.

With the correlation of elements above de scribed, it should be evidentthat when the arm 21 occupies the-position illustrated in Fig. 1 thatweight 35 will be free to move downwardly and thereby maintain the valve2I in elevated position as shown. However, when the arm 21 is movedthrough approximately to the position illustrated in Fig. 2, cable 29will elevate valve l6 and pivot arm 39 in a clockwise direction thereby,through the medium of cable 36,

elevating the weight 35 and causing arm 33 to pivot in acounter-clockwise direction to seat the valve 2| and effect asubstantial closure of the orifice 20.

Assuming that the heat-transfer device II is used for domestic hot waterheating purposes, as hereinbefore indicated, an aquastat as indicatedgenerally at M is disposed in heat responsive relation to the waterheated in the device I]. For exemplary purposes, we have shown theaquastat 4| associated with a pipe 42 which it will be understood isconnected with the heat-transfer device II. The aquastat may comprise aSylphon bellows 43 which expands and contracts in' accordance withchanges in the temperature of the water in the pipe 42. Bellows is connected with a lever, pivoted at one end at 45 and connected at its otherend to a cable 49 which passes over pulleys 41 and 48 and thencedownwardly and is connected to the valve 19. When the temperature of thewater within the heat transfer'device I! or pipe-42 falls to apredetermined minimum, bellows 43 will contract sufficiently to reversethe inclination of the lever arm 44 and thereby, through the medium ofcable 46, elevate valve l9. When this occurs, the gases of combustionmay flow through passage l I and heat-transfer device I1.

One end of a lever arm 49 is connected to cable 46 as indicated at 50.Lever 49 is pivoted intermediat the ends thereof and its other end isconnected to a cable which passes over a pulley 52 and is connected asindicated at 53 to that portion of the cable 36 which lies between thepulleys 31 and 38. Therefore, when the aquastat functions to raise thevalve I9 from its seat, it will also cause lever 49 to pivot in aclockwise direction and through cables 5| and 36 elevate weight 35 andproduce rotation of lever 33 in a counter-clockwise direction sufficientto seat the valve 2| as illustrated in Fig. 3.

From th foregoing, it should be apparent that when either the thermostator the aquastat function to elevate the valve l8 or the valve l9, thevalve 2|, in each case will be moved to its seated position effecting asubstantial closure of the orifice 20 of passage 10. Furthermore, whenboth valves l6 and I9 occupy their closed positions, the valve 2| willbe raised from its seat It will further be understood that thethermostat and the aquastat may so operate as'to cause the valves l6 andI9 to be elevated from their seats during the same period of time and,of couse, when this occurs the valve 2| will occupy its closed positionas it does when either of said valves 16 or I9 is elevated. I

The electrical control system for our furnace and the manner in whichthe various electrical elements are preferably connected in said systernwill best :be understood by referring to Figs. 5 and 6. Power is derivedfrom the main lines 54 and 55 to which are connected conductors 56 and51. Between conductors 56 and 51 is connected the primary of atransformer 58, one end of the secondary of which is connected throughconductor 59 to motor 24, hereinbefore referred to,f'and the other endof the secondary being connected through conductor 60 to a plurality ofcontacts BI, 62 and 63. In the drawings, we have shown the conductor 60as connected to'the supports on which the contacts 6|,- 52 and 63 are,

respectively, pivotally supported and it will understood that thesesupports and the arms bearing said contacts are of electric conductingmaterial. As hereinbefore indicated, motor 24, through the gear reducingmechanism 25, is adapted to rotate shaft 26 on which arm 2'! is mountedand on which are also mounted a plurality of cams. These cams areadapted both to control the circuit to motor 24 and also to control thecircuits to motor 23 of fan 22 and the solenoid 8. I

Contact 6| is mounted on an-arm provided with aboss 64 which is adaptedto engage the surface of-a cam 65 secured on shaft 26. The cam isprovided with a recess 66 which, when the cam occupics the positionshown in Fig. 6, permits the boss 64 to enter and break the electricalcircuit be-- tween the contact 6| and a second contact 61 which isconnected through conductor-6B to one contact 69 of a thermostat 10.However, when the cam 68 occupies the position shown in Fig. 5, contacts61 and 6'! will engage each other! A second cam H which is secured onshaft 26 is provided with a pair of diametrically opposed recesses 12and 13. Contact 62 is mounted on an arm provided with a boss 14 which isadapted to enter either the recess 12 or 13. However, as the camrotates, boss 14 will be forced out of one or the other of said recessesand will ride upon the surface of the cam, holding contact 62 inengagement with a contact 15 which is connected through conductor 16 tothe bi-metallic arm of thermostat 10. Conductor 16 is also connectedthrough conductor 11 to one side of the motor 24. A third cam 18, whichis also secured on shaft 26 is provided with a projection 19 which isadapted to engage the boss onthe arm on which contact 63 is mounted whenit occupies the position shown in Fig. 6 and urge contact 63 intoengagement with a contact 8i which is connected through conductor 82 toa second contact 83 of the thermostat Ill.

The cams and associated contacts, above described, are employed inconjunction with the thermostat 19 to control the operation of motor 24.For example, these elements are illustrated in Fig. 5 in the positionswhich they will occupy after the bi-metallic arm of the thermostat 10,due to a predetermined drop in temperature of the medium to which it isresponsive, has engagedthe contact 83 and has caused motor 24 to rotatearm 27 to open valve l8 and permit gases'of combustion to flow to theheat-transfer device l3. After the iii-metallic arm 10 of the thermostathas engaged contact 69 the motor 24 will rotate the cams and arm 27 tothe positions shown in Fig. 6. It will be understood, of course, thatwhen the arm of thermostat 70 engages either contact 69 or 93 that motor24, in the embodiment illustrated, will operate to rotate the cams andarm 21 through substantially In'Fig. 6, the cams and arms operatedthereby occupy the positions they will be moved to after the thermostatarm had engaged contact 69. In this position thereof, contacts El and6'! and contacts 62 and 15 will be spaced apart but contacts 63 and 8!will lie in engagement with each other. With the parts in thesepositions and assuming that the temperature of the medium, to which thethermostat 70 is responsive falls to a predetermined minimum, causingthe arm of thermostat 10 to engage contact 83, a circuit to mo tor 24will be closed which includes the conductorBO, which is connected to oneside of the secondary of transformer 58 and to contact 63, contact Bi,conductor 82, contact 83 and the bimetallic armin contact therewith,conductor 16 and conductor 11 to one side of motor 24. The motor circuitis completedthrough conductor 59 to theother side of the secondary ofthe transformer 58. 'As the motor 24 rotates the cams from the positionsthereof illustrated in Fig. 6, cam II will force contacts 52 and 15 intoengagement with each other and a parallel circuit will be establishedbetween conductor 60 and conductor I1. Cam H and its associatedcontacts, therefore, insure a continued and complete rotation of thecams through approximately 180 or until therece'ss '13 in cam H is movedto a position permitting the boss i4, associated with the armon whichcontact 62 is mounted, to fall therein and break the circuit betweencontacts 62-and 15. At the same time, of course, the-circuit throughcontacts 63 and 8| will also be broken.

The positions which the cams 65, H and 18 will occupy after having sorotated through 180 are shown in Fig. 5. It will be noted that in thislatter position of the cams, the circuit to contact 83 of the thermostatwill be open and that the parallel circuit through contacts 62 and willalso be open and, therefore, a continued engagement of contact 83 by thearm of the thermostat will not effect a further operation of the motor24. The position of the cams and arm 21, shown in Fig. 5, may beconsidered the on position thereof for house heating purposes. That is,arm 2! has been moved to open the valve l6 and close the valve 2|thereby permitting a flow of the gases of combustion to the heattransfer device [3 which it has been assumed is employed for househeating purposes.

It will be observed that when the cams occupy the positions shown inFig. 5, that cam 65 will hold contacts BI and 61 in engagement with eachother and thereby close a circuit from conductor- 80, through saidcontacts and conductor 68 to contacts 69 of the thermostat. Therefore,when the heat demand has been satisfied and the bimetallic arm ofthermostat Hi engages contact 69, still another circuit to motor 24 willbe completed. This-circuit comprises conductor 60, contacts El and 61,conductor 68, contact 69 and the bi-metallic arm of thermostat 10,conductor 16 and conductor 11 to one side of motor 24. The other side ofthe motor circuit is, of course, completed, through conductor 59. Whenthis circuit is completed, motor 24 will rotate the cams throughsubstantially 180 whereupon the boss 64 associated with the arm on whichcontact 6| is mounted will drop into the recess 66 of cam 65 and openthe circuit to contact 69 of the thermostat and the motor circuit.During this operation of the motor, of course, a parallel circuitbetween conductors 50 and T! will be established through the closing ofcontacts 62 and 1'5. Cam l! and its associated contacts, 62 and 15, isemployed to maintaina circuit to motor 24 once the arm of thermostat lfiengages either the contact 69 or 83 and until the cams are moved throughapproximately 180. 4

A fourth cam, cam 84, is secured on shaft 26 this cam is employed tocontrol the electrical circuit to the motor 23 of the exhaust fan andthe solenoid 8 which operates the valve 1, ar ranged to control theadmission ofair to the ash pit of the furnace. Conductor 56 which isconnected to the main lines is electrically connected with a contact 85mounted on a pivotally supported arm. The conductor 56 is illustrated asconnectedto the support for the arm and it will be understood that thesupport and arm for con-1 tact 155 are of electric conducting material.The arm is provided with a boss 86 which is adapted to engage thesurface of cam 84, and contact 85 is adapted to engage a contact 81 whenthe boss 85 is engaged by a projection 88 on the periphery of cam 8Contact 81 is connected through a conductor 89 to one side of solenoid 8and the fan motor 23 and the other sides of the solenoid and fan motorare connected with conductor 51 which eration of motory24 to open valve[6 and permit a flow of gases of combustion to the heat ex change device13,-cam 84-will close the circuit through contacts and 81 to thesolenoid 8 and fan motor 23 When this occurs, the solenoid 8 willelevate the valve I and permit air to flow to the ash pit of the furnaceand through the fuel bed-thereof. At thesame time, motor 23 will beenergized and will drive fan 22 to produce a forced draft. Ofcourse-when the heat-demand has been satisfied and thermostat 10 effectsan soper-- ation of motor '24 to close the valve 1 6 by rotating the arm-21 to the position illustrated in Fig, 6, contacts 85- and 81 will beparted and the solenoid 8 and fan motor 2 3 de-energized. The aquastat4|, which is mounted in heat responsive relation to the domestic hotwater sup ply which it has been assumed derives its heat from-the ;heat,transferdevice l 1., is operable, as hereinbefore explained, toactuatethe valve 19,; which in tur-n controls the flow of gases throughthe'heat-transfer device I1, and the-valve -2|-. On the arm 44 of theaquastat, to which the valve-operating cable 46 is fastened, is mounteda switch 90. This switch may-be of any desired type and operativelyassociated with the aquastat in any desired manner. For purposes ofillustration, however, we have shown a mercury "tube type of switch. Tothe switch 90 are connected two conductors 91 and 92, the conductor 9|being connected to conductor 89 and conductor 92 being connected toconductor 56. It will be observed that switch 90 is connected in thecontrol circuit in-parallel with the contacts 85 and 8! operated by cam84. Hence, when the aquastat operates to raise the valve 1 9 whereby topermit a flow of gases through the, heat-transfer device I 1., it willalso operate switch 90 to close a circuit therethrough. When the circuitis closed through switch 90, solenoid 8 and fan motor 23 willibeenergized and the furnace will operate under. sub!- stantially the samedraft conditions as when the thermostat l0 operated to effect a flow ofgases of combustion to the heat-transfer device l3.

It will be observed, as hereinbefore pointed out, that the controls forour furnace are arranged to maintain-the valve2| in open position whenallheat demands have beensatisfied. The gases of combustion, therefore,may flow through, the by-pass or passage) and exhaust through thebreeching l5. However, although the gases of combustion are exhausted inthis manner,- there may occur intervals when no heat is de-- manded andunder these idling conditions the temperatures existing in thecombustion chamber of the furnace may fall below that sufficient tomaintain combustion. In orderto maintain the required fuel bedtemperature substantiallyat all: times, weprovide a switch indicated at93 in Figs. 5 and 6 which is embodied in whatmay be generally termed astack switch. Forexample, in one type of stack switch, a helical,lei-metallic strip is employed which is adapted to be associated withthestack or breeching of" ductor 89 and conductor 50. 'I'he switch 93' is,

"therefore, connected in the control circuit in parallel with switch 90and. the contacts actuated by cam 84 and will function to energizesolenoid 8 and fan motor 23 when the temperature conditions to which itis responsive indicate that the fuel bed temperature should be elevated.

In Fig. 4 we have illustrated a modified form of furnace in which butone heat-transfer device is employed as indicated at 96. The furnace isgenerally similar in construction to that illustrated in Fig. 1 and thepassage 9 thereof, through which gases of combustion may flow,communicates with passages 91 and 98. Passage 91 includes theheat-transfer device 96, and the orifice 99 at the top thereofcommunicates with the breeching I5. Likewise, passage 98 forms a bypass,similar to passage I of Fig. l, and communicates through the orifice I00with breeching I5. A valve IN is adapted to form a closure for theorifice 99 and valve I02 is adapted to form a closure for the orificeI00. Assuming that the heat-transfer device 96 is employed for househeating purposes, the control circuit may include the motor 24, itscontrol circuit and associated speed-reducing mechanism and crank arm21, the motor circuit being in the first instance controlled by athermostat, and the control circuit being generally similar to thatabove described.

In' this case, the arm 2'! is connected to a cable I03 which passesupwardly and over pulleys I04 and I 05 and thence downwardly and isconnected to the valve IOI. One end of a lever I06 which is pivotedintermediate the ends thereof is connected to cable I03 as indicated atI01 between the pulley I05 and the valve IOI. Intermediate theconnection III! of arm I06 and its pivotal point, a weight I08 isconnected to said lever. To the other end of said lever is connected a!cable I09 which is fastened to valve I02.

As indicated in full lines in Fig. 4, when the arm 21 is in elevatedposition, valve IOI will lie in closed position and substantiallyprevent the flow of gases of combustion to the heat-transfer device 96while the valve I02 will be elevated and permit the gases to flowthrough the by-pass passage 98. However, when the arm is movedsubstantially through 180 to the dotted line position, the valves IOIand I02 will be moved to the positions illustrated in dotted linesthereby substantially preventing the flow of gases through the by-passwhile permitting a flow thereof through the heat-transfer device. Inthis embodiment of our invention we prefer to provide a solenoid foroperating the valve which controls the flow of air to the ash pit, anexhaust fan, and a heat-responsive witch operable in response to thetemperatures of the products of combustion; the solenoid and the motorfor the exhaust fan being controlled substantially in the mannerhereinbefore described by the thermostat and the said heat-responsiveswitch.

It will be observed that when heat is demanded by ,one or more of themedia to be heated that heat will be supplied to that heat-transferdevice where heat is required. However, when no heat is demanded by anyone of the media, substantially no heat is supplied t-o theheat-transfer device employed in heating the same. Therefore, heat maybe supplied to one or more of a plurality of entirely separate andunrelated Furthermore, it is important to note that under conditions ofno heat demand the temperature of the fuel bed may be maintainedsufilcient- 1y high to sustain combustion at a relatively low rate butwithout supplying heat to the heattransfer devices, while upon any heatdemand the rate of combustion will be increased and the gases ofcombustion supplied to that heat-transfer device where heat is required.In other words, in. our furnace, heat, may be supplied to theheattransfer devices from substantially zero amounts up tothose meetingthe maximum heat-transfer rate of the units or devices. Furnaceoperation of this character is extremely desirable for economic andsatisfactory year-around performance.

As hereinbefore pointed out, the heat-transfer devices of our furnaceare well insulated from eachother, and also, they are remote andpreferably laterally spaced from the combustion chamber and insulatedtherefrom. For example, the rear wall of the combustion chamber is ofinsulating material and extends preferably to an appreciable heightabove the lower end of the fuel bed. The passage 9, furthermore,communicates with the chamber near the top thereof and extends above therear wall, thence downwardly and then laterally into communication withthe preferably, vertically extending passages I0, II and I2. With theabove described insulated construction and arrangement of passages, whenthe valve 1, operated by solenoid 8, and the valve controlling the flowof gases to the heat-transfer device lie in closed position and the fanmotor is deenergized, transfer of heat in all ways to the heat-transferdevice is impeded to such a great extent that substantially no heat issupplied thereto. Furthermore, due to the retention of heat in thecombustion chamber the temperatures above the fuel bed will remainsufiiciently high to support combustion over longer periods undertheab'ove conditions and, therefore, these temperatures will bemaintained sufllciently high over extended periods when no heat isdemanded by the media to be heated at a relatively low, average rate ofcombustion of fuel. wBecause, as above set forth, the heat within thecombustion chamber and above the fuel bed will be retained therein to avery great extent and, further, in view of the fact that thetemperatures in the exhaust passage or breeching of the furnace hereindescribed do not bear any constant relationship to the temperaturesexisting in the combustion chamber, we prefer to place a heat-responsiveswitch or the heat-responsive element thereof in direct heat-responsiverelation to the temperatures within the combustion chamber rather thanin the breeching or exhaust passage of the furnace. This arrangement isillustrated in Fig. 7.

. I In the embodiment illustrated, a passage 0 is provided whichcommunicates with the' combustion chamberin a zone substantiallydirectly abovethe fuel bed an'd'extends through the furnac'e to the topthereof. A closure element II I, which may be of heat-insulatingmaterial, is supin the same way as the switch 93. A helicahbimediawithout affecting in any way the temperature of the other, and hence,more uniform and preciselyeontrolled temperature conditions of themediamay be maintained.

metallic element II3,,for operating the switch proper, depends from theclosure Ilgl withinlthe passage H0. It will: be' observed. that theheatresponsive bi-metallic element H3 is exposed to the heat radiated--directly from the'fuel burning inthe combustion chamber itself and,therefore, a precisecontrol of the operation of thefurnace is obtainedunder those conditions where no heat is demanded by the media to beheated whereby the temperature of the fuel bed will be maintainedsufficiently high to sustain continued combustion of the fuel but onlyatsubstantially the minimum rate of combustion over periods during whichthese conditions exist, which is necessary so to'support combustion.

It is to be understood, of course, though we have illustrated anddescribed our furnace as comprising heat insulating material for thepurposes above set forth, the walls of the combustion chamber andpassages are lined. with fire brick or like heat-resistant material.

While we have described our invention in its preferred embodiments, itis tobe understood that the Words which we, have used are words: ofdescription rather than of limitation. Hence,

changes Within the purview of the appended claims may be made withoutdeparting from the true scope and spirit. of our invention in itsbroader aspects.

What we claim is: r. l. A furnace of the character described comprisinga combustion chamber within which fuel may burn, means defining aplurality of passages communicating with said combustion chamber andthrough which the gases of combustion may flow, one of said plurality ofpassages constituting a by-pass, a heat-transfer device includ'ed'in afirst of said plurality, of passages and a heattransfer device includedin a secondof said plurality of passages, said heat-transfer devicesbeing adapted respectively to supply heat to. a. first and secondmedium, a valve operatiyely 'associated with each of said; plurality ofpassages, valve-operating means, a first, heat-responsive means reponsive to the temperatureofsaid first medium and a secondheat-responsive means re-r sponsive to the temperature of said secondmedium for controlling respectively the valveas; sociated with saidfirst and-second passageand both of said heat-responsive means, beingoperable'to control the 'valve associated with said by?) pass passage toclose the by-pass valve,v when, either of the other valves are openedand tqopen, said by-pass valve when both of theptherllalves: are closed.

2. A furnace of the character? described comprising a combustion chamberwithinwhich, fuel may burn, means defining. abluralityof passagescommunicating with said combustion 'chamber and through which the gasesofcombustion may. flow, one of said passages including a. heatftransferdevice adapted to supply heat to a medium, means for controlling theflo'woffg lses through said plurality of passages including a,heat-responsive means responsive'to the temperature of. said medium,said flow control 'means'being 'oper; able to pass substantially all" ofsaid gases to said heat-transfer device whenaheat demand exists and toprevent a how of gases to saidheat transfer deviceand to exhaust saidga'sesthrou'gh a second of said passages when'no heat demand exists,afan arranged to produce a forced new of gases of combustion, anelectric motor for" driving said fan, said motor being controlled by'said heat-responsive means, and means including a switch andaheat-responsive, actuating element therefor disposed in heat responsiverelation to heat generated in said combustion chamber for controllingsaid motor.

communicating with said combustion chamber and through which the gasesof combustion may flow, one of said passages including a heat-trans ferdevice adapted to supply heat to a medium,

means for controlling the flow of gases through said plurality ofpassages including a heat-responsive means responsive to the temperatureof said medium, said flow control means being operable to passsubstantially all of said gases to said heat-transfer device when'a heatdemand exists and to prevent a flow of gases to said heattransfer deviceand to exhaust said gases through a second of said passages when no heatdemand exists, a fan arranged to produce a forced flow of gases ofcombustion, an electric motor for driving said fan, said motor beingcontrolled by said heat-responsive means, and means including a switchand a heat-responsive, actuating element therefor disposed in directheat responsive relation to heat radiated from the fuel burning in saidcombustion chamber for controlling said motor. r 4. A furnace of thecharacter described comprising a combustion chamber having a gratetherein adapted to support a bed of fuel, means defining a plurality ofpassages communicating with said combustion chamber and through whichthe gases of combustion may flow, one of'said passages including aheat-transfer device adapted to supply heat to a medium, means forcontrolling the flow of gases through said plurality of passagesincluding a heat-responsive means responsive to the temperature of saidmedium, said flow control means being operable to pass substantially allof said gases to said heat-transfer device when a-heat demand exists andto prevent a flow of gases to said heat-transfer device and to exhaustsaid gases through a second of said passages when no heat demand exists,a fan arranged to produce a forced flowof gases of combustion, anelectric motor for driving said fan, means forming an air inlet openingfor the admission of. air beneath said grate, a valve for controllingthe admission of air through saidair inlet opening, electrical means foroperating said valve, said motor and electrical means being controlledby said heat-responsive means to open said valve whereby to admit airbeneath said grate when said motor is energized and to close said valvewhen the motor is de-energized, and means responsive to heat generatedin said combustion chamber for controlling said motor and electricalmeans.

5. A solid fuel-burning furnace of the character described comprisingacombustion chamber havinga grate thereinup'on which solid fuel may burn,means defining a plurality of passages communicating with saidcombustion chamber above the grate therein and through which the gasesof combustion may flow, a first of said plurality of passages includinga'heat-transfer device adapted for house-heating purposes and a forcedflow of gases of combustion, and means responsive to. the tem erature otthe medium heated by i said heat-transfer device for-controlling theoperation of said operating'means and said means for producing a forcedflowof gases; whereby combustion gases flow through said'heat-transferdevice only when a 'heatfdemand for house heating purposes exists.

" 6, A solid fuel-burning furnace of the character described comprisinga combustion chamher having a'grate therein upon Whichsolid fuel mayburn, means defining avplurality of passages communicating-With saidcombustion chamber above the grate therein and through which the gasesof combustion may flow, a-first of said plurality of passages includinga heat-transfer device adapted for house-heating purposes and a secondof said passages forming a by-passfor the direct exhaust of combustiongases .from said combustion chamber, means for controlling the flow ofgases through said plurality of' passages, said control means beingoperable substantially to'prevent the flow of gases through one of saidpassages when actuated to permit a flow thereof through the otherpassage, means for operating said control means, means for producing aforced flow of gases of combustion, means'forming an air inlet openingfor the admission of air beneath said grate, a valve for controlling theadmission of said air and operating means therefor, andmeans responsiveto the temperature of the medium heated by said heat-transfer device forcontrolling the operation of said control-operating means, saidfiow-producing means and said valve-operating means; whereby combustiongases flow through said heat-transfer device only when a heat demand forhouse heating purposes exists. 1

-7. A solid fuel-burning furnace of the character describedcomprising acombustion chambervhaving a'grate'th'erein-upon which fuel may burn,means defining a plurality of passages communicating with saidcombustion chamber above said grate and through which the gases ofcombustion may flow, a heat-transfer device included in one of saidplurality of passages and adapted to supply heat to a medium forhouse-heating purposes, a heat-transfer device included in a second ofsaid plurality of passages and adapted to supply heat for domestic hotwater supply purposes, and a third of said plurality of passagesconstituting a by-pass, valve means for controlling the fiow of gases ofcombustion to said heat-transfer devices and through said by-pass, saidvalve means being operable substantially to prevent the flow of gases tosaid heat-transfer devices, and means including a first and secondheat-responsive means responsive respectively to the temperatures ofsaid medium and said domestic hot water supply to which heat istransferred by said heat-transfer devices for operating said valvemeans; said valve means being operable to positions permitting at alltimes an exhaust of said gases from the combustion chamber but to aposition substantially preventing the passage of said gases through saidby-pass when actuated to pass said gases to either or both of saidheat-transfer devices and to a position permitting the passage of gasesthrough said by-pass when preventing the passage thereof to both of saidheat-transfer devices.

8. A solid fuel-burning furnace of the character described comprising acombustion chamber having a grate therein upon which fuel may burn,means defining a plurality of passages communicating with saidcombustion chamber above said grate. and through which .the gases ofcombustion may flow, a heat-transfer device included in one of saidplurality of passages and adapted to supply heat to. a medium forhouseheating purposes, a heat-transfer device included in a second ofsaid plurality of passages and adapted to supply. heat for domestic hotwater supply purposes, and a third of said plurality of passagesconstituting a by-pass, valve means for controlling the flow of gases ofcombustion'to said heat-transfer devices and through said by'-' pass,said valve means being operable substantially to prevent the flow ofgases to said heattransfer devices, means for providing a forced flow ofgases of combustion, and means including afirst and secondheat-responsive .means' responsive respectively to the temperatures ofsaid medium and hot water supply for operating said valve means and saidmeans for producing a forced fiow of gases; said valve means being soconstructed and arranged as to prevent a flow of gases through saidby-pass when passing said gases to one or both of said heat-transferdevices and to pass said gases through said by-pass when preventingtheir flow to both heat-transfer devices.

9. Asolid fuel-burning furnace of the character described comprising acombustion chamber having a grate therein upon which fuel may burn,-means defining a plurality of passages communicating with saidcombustion chamber above said grate and through which the gases ofcombustion may flow, a heat-transfer device included in one of saidplurality of passages and adapted to supply heat to a medium forhouseheating purposes, a heat-transfer device included in a second ofsaid plurality of passages and adapted to supply heat for domestic hotwater supply purposes, and a third of said plurality of passagesconstituting a-by-pass, valve means for controlling the flow of gases ofcombustion to said heat-transfer devices and through said bypasspassage, and means including a first and second heat-responsive meansresponsive respectively to the temperatures of said medium and saiddomestic hot water supply for operating said valve means; said valvemeans being so constructed and arranged as to prevent a flow of gasesthrough said by-pass when passing said gases to one or both of saidheat-transfer devices and to pass said gases through said by-pass whenpreventing their flow to both heat-transfer devices.

10. A solid fuel-burning furnace of the character described comprising acombustion chamber having a grate therein upon which fuel may burn,means defining a plurality of passages communicating with saidcombustion chamber above said grate and through which the gases ofcombustion may flow, a heat-transfer device included in one of saidplurality of passages and adapted to supply heat to a medium forhouseheating purposes, a heat-transfer device included in a second ofsaid plurality of passages and adapted to supply heat for domestic hotwater heating purposes, and a third of said plurality of passagesconstituting a by-pass, valve means for controlling the flow of gases ofcombustion to said heat-transfer devices, means for producing a forcedfiow of gases of combustion, means including a first and secondheat-responsive means responsive respectively to the temperatures ofsaid medium and hot water supply for operating said valve means andcontrolling said means for producing the forced fiow of gases; saidvalve means being so constructed and arranged to prevent a flow of gasesthrough said by-pass when passing said gases to one or both of saidheattransfer devices and to pass said gases through said by-pass whenpreventing their flow to both heat-transfer devices, and meansresponsive to heat generated in said combustion chamber for controllingsaid flow-producingv means.

11. A solid fuel-burning furnace of the character described comprising acombustion chamber having a grate therein upon which solid fuel mayburn, means defining a plurality of passages communicating with saidcombustion chamber above said grate and through which the gases ofcombustion may now, one of said passages in cluding a heat-transferdevice adapted to supply heat to a medium, means for controlling theflow of gases through said plurality of passagesv including aheat-responsive means responsive to the temperature of-said medium, saidflow-con trol means being so constructed and arranged as to prevent aflow of gases through a first of said passages when passing gasesthrough a second thereof and to pass gases through said first passageWhen preventing their flow through said second passage, means forproducing a forced flow of gases of combustion, the operation of saidlast mentioned means being controlled by said heat-responsive means, andmeans responsive to heat generated in said combustion chamber forcontrolling the operation of said flow-producing means.

12. A solid fuel-burning furnace of the character described comprising acombustion chamber having a grate therein upon which solid fuel mayburn, means defining a plurality of passages ranged as to pass gases ofcombustion through one of said passages when preventing their flow toboth of said heat-transfer devices, means for producing a forced flow ofgases of combustion, the operation of said last mentioned means beingcontrolled. by said heat-responsive means, and meansv responsive to heatgenerated. in said combustionr chamber for controlling the operation ofsaid flow-producing means.

13. A solidv fuel-burning furnace of the character described comprisinga combustion chamber having a grate therein upon which fuel may burn,means defining a plurality of passages com municating with saidcombustion chamber above said grate. and. through which the gases ofcom.-. bustion may flow, a heat-transfer device included in one of saidplurality of passages and adapted tov supply heat to a medium forhouse-heating purposes; a. heat-transfer device included in a second ofsaid plurality of passages and adapted to supply heat for domestic hotwater supply purposes; and a third of said plurality of pas sagesconstituting a by-pass, and valve means including: operating meanstherefor for controlling the flow of gases of combustion to said heattransfer devices and through said by-pass; said valve means being soconstructed and arranged as to substantially entirely out off the flowof said gases through said by-pass when actuated to pass said gases toeither or both of said heattransfer devices and to permit the flow ofsaid gases: through said by-pass when actuated to pre-- vent a. flow ofgases to both heat-transfer devices:

WARREN S. BLAUVELT. NOLAN A. CURRY.

